Introduction

The Canon EF 20-35mm f/3.5-4.5 USM was Canon´s first attempt to provide
an ultra-wide lens to the masses. It was introduced back in 1993 and possibly
it has been discontinued recently (no clear information here yet).
Regarding its initial release date it is obviously a full frame lens but as usual
this review focuses on the performance on an APS-C DSLR
where the field-of-view is equivalent to 32-56mm - a rather limited
zoom range here.

The optical construction is made of 12 elements in 11 groups without any
special elements.
Its aperture mechanism features just 5 aperture blades so a pleasing
bokeh was probably not on the design priority list nor is it really
needed for the majority of applications of such a lens.
The minimal focus distance is 0.34m resulting in a max. magnification
of 1:7.7 at 35mm.
Typical for many ultra-wides it is comparatively short but fat with a
size of 84x69mm and a low weight of just 340g.

The build quality of the lens is quite decent based on fairly good quality
plastics but it´s not comparable to a Canon L grade lens - it´s not
quite as tight. It´s a true IF lens so the physical length of the lens
remains constant and unlike the newer Canon L zooms in this range there´s
no moving inner lens tube.
The front element does not rotate so using a polarizer remains easily possible.
The rubberized zoom control ring operates pretty smooth and reasonably well
damped. The focus ring is quite narrow as typical for many consumer grade
Canon lenses. The lens features a very fast and virtually silent ring-type
USM drive. Full-time manual focusing (FTM) remains possible in one-shot AF mode.

One interesting feature is the flare cutting diaphragm which has been
positioned just behind the large front element (see the right product
shot above). Certainly a good idea because wide angles are quite a bit
more prone to flare than conventional lenses. The concept has been
further developed in some of the successors where this diaphragm moves
according to the zoom position positioned in the middle portion of
these lens so it´s not as obvious.